Glossary Terms Beginning A

0-9 : A : B : C : D : E : F : G : H : I : J : K : L : M

N : O : P : Q : R : S : T : U : V : W : X : Y : Z

A: Ampere (or amp): measurement of electrical current.
AC: Alternating current: type of electrical current.
AC-3: See Dolby AC-3.
Access: The general term for the ability of a telecommunications user to make use of a network.
ADC: Analogue-to-digital conversion: process of converting analogue signals to a digital representation. DAC represents the reverse translation.
Ad hoc capacity: Capacity available for bookings on a temporary basis; see Occasional capacity.
ADPCM: Adaptive differential pulse code modulation.
Algorithm: Refers to the computational code used to compress or decompress a signal.
AM: Amplitude modulation.
Amplifier: Device used to increase the power of an electronic signal.
Amplitude modulation: Process where a baseband message signal modulates (alters) the amplitude and frequency of a high-frequency carrier signal, which is at a nominally fixed frequency, so that the carrier signal varies in amplitude.
Analogue: Signal which can take on a continuous range of values between a minimum and a maximum value; method of transmitting information by continuously variable quantities, as opposed to digital transmission, which is characterized by discrete 'bits' of information in numerical steps.
ANIK: Canadian domestic satellite system.
ANSI: American National Standards Institute (US).
Antenna: Device for transmitting and receiving radio waves; in SNG, the directional parabolic antenna used for satellite transmissions.
AOR: Atlantic Ocean Region: describes coverage area of a satellite.
Aperture: Cross-sectional area of a parabolic antenna.
Apogee: The point in a satellite's orbit when it is furthest away from the Earth.
Artifacts: Imperfections in a digital signal caused by the compression process.
ASI: Asynchronous serial interface: DVB compliant signal.
ATM: Asynchronous transfer mode: division of digital signals into small packets and transmitted in small, fixed-size data 'cells'.
Atmospheric losses: Losses caused by the travel of the signal through the atmosphere - encountered on both the uplink and the downlink.
Attenuation: Loss in power of electromagnetic signals between transmission and reception points.
Attitude control: Orientation of the satellite in relationship to the Earth and the Sun.
Audio sub-carrier: An extra carrier typically between 5 and 8 MHz carrying audio information on top of a video carrier.
Automatic frequency control: AFC: circuit which automatically controls the frequency of a signal.
Automatic gain control: AGC: circuit which automatically controls the gain of an amplifier so that the output signal level is virtually constant for varying input signal levels.
Availability: The percentage of time over a year that a satellite link will be received successfully. Not particularly applicable to SNG uplinks.
Azimuth: Angle of rotation (horizontal) that a parabolic antenna must be rotated through to point to a specific satellite in a geosynchronous orbit; the compass bearing of the satellite in the horizontal plane from a point on the Earth's surface.